Efforts directed at improving air quality and increasing energy production from renewable resources have resulted in renewed interest in alternative fuels, such as ethanol and butanol, that might replace gasoline and diesel fuel, or be used as additives in gasoline and diesel fuel.
Methods for producing 1-butanol from ethanol are known. For example, 1-butanol can be prepared by condensation from ethanol over basic catalysts at high temperature using the so-called “Guerbet Reaction” (see for example, J. Logsdon in Kirk-Othmer Encyclopedia of Chemical Technology, John Wiley and Sons, Inc., New York, 2001).
U.S. Pat. No. 6,323,383 describes a method of synthesizing 1-butanol from ethanol using a catalyst made of calcium phosphates, particularly low-crystalline calcium phosphates singly or as a mixture, wherein the Ca/P mol ratio is adjusted to from 1.4 to 1.8, as it is, or a catalyst by carrying an activation metal or the oxide thereof on the catalyst such that the (Ca+metal)/P mol ratio becomes from 1 to 2.
Published US Patent Application 2007/0255079 A1 discloses a process for producing, from ethanol as a raw material, higher molecular weight alcohols having an even number of carbon atoms, such as 1-butanol, hexanol, octanol and decanol. The higher molecular weight alcohols are produced from ethanol using calcium phosphate-based compounds such as hydroxyapatite Ca10(PO4)6(OH)2, tricalcium phosphate Ca3(PO4)2, calcium monohydrogen phosphate CaHPO4.(0-2)H2O, calcium diphosphate Ca2P2O7, octacalcium phosphate Ca8H2(PO4)6.5H2O, tetracalcium phosphate Ca4(PO4)2O, or amorphous calcium phosphate Ca3(PO4)2.nH2O as a catalyst, the contact time being 0.4 second or longer.
Hydroxyapatite compositions comprising an alkaline earth metal other than calcium, or a mixture of more than one alkaline earth metal, are also known. For example, a comparison of preparation procedures of barium hydroxyapatites has been reported (S. Sugiyama, T. Nakanishi, H. Hayashi, J. B. Moffat, Phos. Res. Bull. Vol. 8, pp 23-30 (1998). The preparation and characterization of phosphate and arsenate apatites of strontium and their solid solutions is described (G. George, S. K. Gupta, P. V. R. Rao, T. S. B. Narasaraju J. Mat. Sci. Vol. 22, pp 2274-2276 (1987)). The preparation of barium-strontium hydroxyapatites is described by A. Yasukawa et al. (A. Yasukawa, M. Kidokoro, K. Kandori, T. Ishikawa, J. Colloid Interface Sci., Vol. 191, pp 407-415 (1997)). The coprecipitation of strontium with hydroxyapatite (O. Fujino, Bull. Chem. Soc. Jpn. Vol. 48, pp 1455-1458 (1975)), and the preparation of hydroxyapatite loaded with strontium (S.-C. Liou, S.-Y. Chen, H.-Y. Lee, J.-S. Bow, Biomaterials, Vol. 25, pp 189-196, (2004)) have also been disclosed. The latter two references refer to mixed calcium/strontium hydroxyapatites.
New catalyst compositions useful in a process for producing butanol from a reactant stream comprising ethanol are continually sought. Catalyst compositions which can provide high conversions of ethanol to butanol are desired. Also desired are catalyst compositions which provide good selectivity to butanol, as well as catalyst compositions having long catalytic lifetimes. Additionally, processes to produce butanol and which employ such new catalyst compositions are desired for the economic benefits they can offer.